Hydrochemical Characterisation and Assessment of Groundwater Suitability for Drinking and Irrigation Purposes in Sângeorz-Băi Area, Bistrița-Năsăud County (Romania)

Abstract

Groundwater quality is a key factor and a critical determinant of public health, agriculture, and socio-economic development, particularly in regions where private wells and mineral springs constitute the primary water sources. This study presents an integrated hydrochemical, radiological, and toxicological assessment of groundwater in the Sângeorz-Băi area, Romania, a spa region where mineral waters hold both therapeutic and economic significance. Samples from mineral springs, the municipal supply system, and private wells were analyzed to evaluate compliance with national and international standards and to assess their suitability for drinking, therapeutic, and agricultural purposes. The results reveal distinct hydrochemical contrasts between sources. Mineral springs are characterized by elevated salinity, hardness, and Na–HCO₃ facies, whereas the municipal network and private wells are dominated by Ca–HCO₃ facies. More than half of the private wells exceeded permissible limits for NO₃⁻, NO₂⁻, NH₄⁺, Pb, and Fe, with one well posing a significant nitrite-related health risk. Trace metal analysis indicated localized enrichment in Cu, Fe, and Pb. Radon and radium activities generally complied with regulations, although radium occasionally exceeded the more stringent WHO guidelines. Seasonal variation was minimal, reflecting stable groundwater chemistry. Health risk and irrigation assessments suggest that municipal supply water is largely safe for consumption, while private wells require targeted monitoring and mitigation. Despite elevated Na⁺ and Cl⁻, mineral springs retain therapeutic value under controlled use. This study provides a replicable framework for groundwater quality assessment in spa regions and offers critical insights for public health protection, sustainable tourism, and agricultural resilience.

1. Introduction

As the global population continues to grow, the demand for drinking water has also been increasing, particularly over the past few decades. This rising demand for water, both for domestic and agricultural purposes, has led to the overexploitation of groundwater resources, especially in arid and warm climates. Numerous studies have examined groundwater quality [1,2,3,4,5,6,7,8,9,10,11,12]. Continuous monitoring of groundwater is crucial, as it helps identify potential toxic elements, their sources, mobility, and impact on both human health and environmental quality. The chemical composition of groundwater is closely linked to various factors, including meteorological conditions, geographical features of the area, geological characteristics of the aquifer, and the contact time between water and rock. Hydrochemical investigation of aquifers provides valuable data that local authorities can use for managing groundwater resources [13] or implementing remediation strategies [14].

The spatial and temporal distribution of water resources in Romania are primarily influenced by the country’s geographical location in the temperate-continental climate zone and by the presence of the Carpathian Mountain range. Over the past few decades, Romania has experienced a growing demand for water across various sectors, including drinking, industry, agriculture, fish farming and tourism. Water consumption increased from 14.4 billion m³ in 1975 to 46 billion m³ between 2010 and 2015 [15]. Groundwater resources are estimated at 11 billion m³ per year, with approximately 80% of these resources located in hilly and plateau regions. The Carpathian and Sub-Carpathian areas are home to significant mineral water resources, which are linked to volcanic activity and the presence of salt, oil, gas, and coal deposits. More than 2000 springs are found in these areas, the majority of which are of chloro-sodic, sulphurous-sulphate and carbonated types [15].

Groundwater represents a vital component of the freshwater system and is highly vulnerable to chemical contamination from both natural and anthropogenic sources. This study demonstrates the generally good quality of several groundwater sources in an historic spa resort area of Romania, underscoring the need to preserve their integrity while also recognizing the economic potential of mineral springs for bottling, commercial distribution, and therapeutic applications. These resources constitute a valuable asset that can contribute to the sustainable development of the region. The primary objectives of this study were: (1) to characterize the hydrochemical properties of groundwater in Sângeorz-Băi; (2) to assess its suitability for drinking and irrigation; and (3) to evaluate the temporal stability of its chemical composition.

2. Materials and Methods

2.1. Study Area

Sângeorz-Băi is located in Bistrița-Năsăud County, along the Someșul Mare River in the southern Rodna Mountains, approximately 56 km from the city of Bistrița. The local economy is primarily based on tourism, forestry, and agriculture. Geologically, the area belongs to a subvolcanic district in the inner Eastern Carpathians (northern Romania) [16]. The study site is situated within the volcanic segment of Țibleș–Rodna–Bîrgău, where rocks have been dated between 8.0 and 11.4 Ma [17].

This region is characterized by magmatic intrusions into diverse lithologies, including the crystalline units of the Rodna Mountains—dominated by garnet-bearing micaschists, paragneisses, and amphibolites—as well as the sedimentary successions of the Bârgău Mountains, consisting of conglomerates, limestones, marls, sandstones, and argillaceous marls [18,19]. The igneous suite is weakly evolved and comprises two main groups: (1) basic rocks such as amphibole microgabbro and amphibole- and clinopyroxene-bearing basaltic andesite, and (2) intermediate rocks including amphibole andesite, plagioclase andesite, and leucocratic andesite [20]. According to established classifications [20,21], most igneous rocks in the Rodna–Bârgău area belong to the calc-alkaline or low-iron subalkaline series. Contacts between magmatic intrusions and sedimentary host rocks are typically marked by hornfels zones and, less frequently, by breccias [17]. Intrusive bodies include laccoliths, sills, stocks, and dykes [18,19,22], which are interpreted as remnants of magma chambers that once sustained subaerial volcanic activity [23].

The climate of the region is characterized by a mean annual temperature of approximately 7.5 °C. Prevailing winds predominantly originate from the northwest, west, and southwest. In Bistrița-Năsăud County, annual precipitation averages 650–700 mm in the valleys and around 800 mm on the hilltops, with a maximum between May and August and a minimum during winter [24].

The mineral waters of Sângeorz-Băi have been renowned for their therapeutic properties since the 17th century. The first documented mention of these waters dates back to 1777, by Mattyus cited in [25], though they were likely known even earlier. The earliest physico-chemical analyses were conducted in the late 19th century [26,27]. In 1858, a spa resort was established in the area, transforming it into a tourist destination. By 1879, the mineral waters began to be commercially exploited and were bottled under the brand name “Hebe”—a bicarbonate-chloro-sodic water recommended for treating digestive, liver, and reproductive system disorders. Currently, the mineral springs are no longer in use and are in an advanced state of degradation.

In Sângeorz-Băi locality, groundwater serves as the primary source of drinking water. Residents have access to potable water through a local distribution network and private wells. The local distribution system is supplied by 14 boreholes, ranging in depth from 8 to 17 m, with flow rates varying between 7 and 25.2 m³/h. The daily water demand in Sângeorz-Băi ranges from 1429.1 to 1728.9 m³/day, with an average consumption of approximately 1571.6 m³/day.

2.2. Sampling and Analytical Methods

To assess the quality of groundwater in the Sângeorz-Băi area, a total of 60 samples were collected: 16 from mineral springs, 14 from local water supply network, and 30 from private wells (Figure 1). To evaluate the chemical stability of the groundwater, two sets of samples were taken—one in autumn (October 2017) and another in spring (May 2018). Sampling was conducted in accordance with standard procedure outlined by national and international protocols [28,29].

The following physico-chemical parameters were analyzed: pH, redox potential (Eh—mV), electrical conductivity (EC—µS/cm), total dissolved salts (TDS—mg/L), and salinity (‰). The measurements were taken in situ using a pre-calibrated portable multiparameter device (WTW Multi 350i, Weilheim, Germany).

The samples were filtered using 0.45 µm nylon syringe filters and transferred into clean polyethylene vials, which had been thoroughly pre-rinsed before use. Samples intended for cation and metal analysis were acidified to approximately pH 2 using HCl and HNO₃, respectively, to prevent precipitation or adsorption during storage. All samples were stored in dark, refrigerated conditions at 4 °C. Prior to ion analysis, the samples were diluted with ultrapure water (18.2 MΩ·cm) to an electrical conductivity of approximately 100 µS/cm, in order to protect the chromatographic column and prevent detector oversaturation.

The major dissolved ions (F⁻, Cl⁻, Br⁻, NO₂⁻, NO₃⁻, PO₄³⁻, SO₄²⁻, Na⁺, K⁺, NH₄⁺, Mg²⁺, Ca²⁺) were analyzed using an ion chromatography system (Dionex 1500 IC, Sunnyvale, CA, USA) equipped with IonPac AS23/CS12A columns (4 × 250 mm), IonPac A23G/CG12A precolumns (4 × 50 mm) and a self-regenerating suppressor (ASRS/CSRS ultra II, 4 mm (Dionex, Sunnyvale, CA, USA) coupled to a conductivity detector. The eluents used were 4.5 mM Na₂CO₃/0.8 mM NaHCO₃ for anionis and 20 mM methanesulfonic acid for cations, with a flow rate of 1 mL/min. The analysis of CO₃²⁻ and HCO₃⁻ was performed using a gravimetric method, involving titration with 0.1 M HCl in the presence of phenolphthalein and methyl orange as indicators.

The total metal content (Ni, Cd, Cr, Pb, Zn, Cu, Fe, Mn) was determined by atomic absorption spectrometry (AAS), using a ZEEnit 700 system (Analytik Jena, Jena, Germany) equipped with an air—acetylene burner, a graphite furnace, and a specific hollow—cathode lamp for each metal.

Radon and radium concentration in water were measured using a LUK-3A device specifically adapted for liquid samples (Jirí Plch—SMM (Prague, Czech Republic)). Radon measurements were performed with a LUK-VR system equipped with Lucas cells and a specialized apparatus for dissolved gas extraction [30]. Water samples were analyzed in the laboratory after reaching a temperature of 20 °C, employing the Lucas cell scintillation method as described by [31]. To determine radium concentration, water samples were stored in the laboratory for 30 days to allow for secular equilibrium between radium and its decay product radon, ensuring equal concentrations of both isotopes. Following this period, radium concentration was measured using the same Lucas cell scintillation technique [31,32].

2.3. Water Suitability for Drinking Usage

The potential health risk associated with the ingestion of chemical compounds (dissolved ions and metals) through drinking water was assessed by calculating the estimated daily intake (EDI), expressed in mg/kg body weigh/day [33,34] using the following formula:

$$\mathrm{E}\mathrm{D}\mathrm{I}={\displaystyle \frac{C·IR}{BW}},$$

(1)

where C—element concentration in water (mg/L); IR—water ingestion rate (2 L/person/day); and BW—average adult body weight (60 kg for an adult person in Europe [34]).

To assess the potential health impact on consumers due to radon and radium intake through drinking water, the annual effective dose (Sv) resulting from water ingestion was estimated, as follows:

$$E=K·C·IR·t,$$

(2)

where E—effective dose from ²²²Rn (²²⁶Ra) ingestion (Sv); K—conversion factor of ²²²Rn (²²⁶Ra) ingesting dose (Sv/Bq); C—concentration of ²²²Rn (²²⁶Ra) in water (Bq/L); IR—water ingestion rate for adults (1 L/person/day); t—duration of consumption (365 days) [35,36].

The dose conversion factors for adults used in the assessment of radon exposure were those recommended by the United Nations Scientific Committee on the Effects of Atomic Radiation [35], at 1.0 × 10⁻⁸ Sv/Bq, and by the National Council on Radiation Protection and Measurements [37], at 0.35 × 10⁻⁸ Sv/Bq. The committed effective dose from ²²⁶Ra ingestion was calculated by multiplying the annual intake activity by the corresponding dose conversion factors: 2.8 × 10⁻⁷ Sv/Bq [36] or 2.2 × 10⁻⁷ Sv/Bq [38].

2.4. Water Suitability for Agricultural Usage

Elevated concentration of Na⁺, Cl⁻, Ca²⁺, Mg²⁺, and HCO₃⁻ in irrigation waters can adversely affect soil structure and permeability, potentially leading to significant stress on crops. To assess the suitability of water from private wells and the local supply network for irrigation purposes, the following indices were calculated: Sodium Adsorption Ratio (SAR) [39], Sodium Percentage (%Na) [40], Kelly’s Ratio (KR) [41], Residual Sodium Carbonate (RSC) [42], Magnesium Adsorption Ratio (MAR) [43], and Permeability Index (PI) [44]. All ion concentrations were expressed in milliequivalents per liter (meq/L):

$$SAR={\displaystyle \frac{{Na}^{+}}{\sqrt{\frac{{Ca}^{2+}+{Mg}^{2+}}{2}}}},$$

(3)

$$\%Na={\displaystyle \frac{{Na}^{+}+K^{+}}{{Ca}^{2+}{+{Mg}^{2+}+Na}^{+}+K^{+}}}·100,$$

(4)

$$KR={\displaystyle \frac{{Na}^{+}}{{Ca}^{2+}+{Mg}^{2+}}},$$

(5)

$$RCS=\left({CO}_3^{2-}+{HCO}_3^{-}\right)\left({Ca}^{2+}+{Mg}^{2+}\right),$$

(6)

$$MAR={\displaystyle \frac{{Mg}^{2+}}{{Ca}^{2+}+{Mg}^{2+}}}·100,$$

(7)

$$PI={\displaystyle \frac{{Na}^{+}+\sqrt{{HCO}_3^{-}}}{{Ca}^{2+}+{Mg}^{2+}{+Na}^{+}}}·100.$$

(8)

The SAR, %Na and KR indices are used to evaluate the potential hazard posed by excessive Na⁺ in irrigation water. Sodium ions can be adsorbed by soil clay particles, displacing Ca²⁺ and Mg²⁺ ions, which leads to reduced soil permeability and impaired plant growth [45,46]. Additionally, Na⁺ can react with CO₃²⁻ to form alkaline soils or with Cl⁻ to form saline soils—both conditions having a significant adverse effect on crop productivity [47].

RCS estimates the impact of elevated carbonate concentration in irrigation water, particularly the removal of Ca²⁺ and Mg²⁺ from the soil solution, which can significantly alter soil physical properties [45]. When the combined concentration of Ca²⁺ and Mg²⁺ exceeds that of CO₃²⁻, Na₂CO₃ levels tend to decrease. Conversely, an excess of CO₃²⁻ and HCO₃⁻ can lead to the precipitation of Ca²⁺ and Mg²⁺ in the soil, deteriorating soil structure and enhancing the mobilization of Na⁺ [48]. High RCS values are indicative of increased sodium adsorption in the soil, which can negatively impact soil quality [48]. MAR characterizes the balance between Mg²⁺ and Ca²⁺ in groundwater. Elevated levels of Mg²⁺ in irrigation water can disrupt soil chemistry and structure, ultimately reducing crop production [49].

PI is a useful index used to assess the suitability of irrigation water based on the concentrations of Na⁺, Ca²⁺, Mg²⁺, and HCO₃⁻, as these ions influence soil permeability and water infiltration capacity.

3. Results and Discussions

Table 1 presents a synthetic statistic of the analyzed parameters, comparing them to the values recommended by the national [50,51,52] and international [53] legislation.

3.1. Physico-Chemical Parameters

The pH of the water samples ranged from slightly acidic to neutral (6.5–7.1) in mineral spring, and from slightly acidic to slightly alkaline in local supply networks (6.8–7.5) and private wells (6.5–7.6) [54]. In all cases, the pH values fell within the acceptable limits established by national regulations (6.5–9.5, [50]) and international guidelines (6.5–8.5, [53,55]) (Table 1). Redox potential values were generally negative and showed an inverse correlation with pH, consistent with typical groundwater chemistry behaviour.

The pH values we observed (6.5–7.6 across all water types) are consistent with the typical range for Carpathian springs and shallow wells, which usually vary between slightly acidic and slightly alkaline, depending on carbonate buffering capacity and local lithology [56,57]. Recent studies in Apuseni Mountains (Romania) and Low Tatra (Slovakia) reported groundwater pH mostly between 6.7 and 7.5, supporting the view that our samples fit well into the regional pattern [12,56,58].

Table 1. Summary of the analyzed parameters and the permissible limits for drinking water as specified by Romanian regulation and WHO guidelines (the bold values represent the permissible limits exceeding).

Parameter	Mineral Springs	Local Network	Private Wells	Romanian Standard (1,2)	WHO Standard (3)
pH	6.5–7.1 (6.8)	6.8–7.5 (7.1)	6.5–7.6 (7.2)	6.5–9.5	6.5–8.5
Eh (mV)	−24.9–11.8 (−6.5)	−47.7–7.9 (−24.3)	−54.3–7.5 (−29.9)	-	-
EC (µS/cm)	5280–7720 (6773)	141.8–447.1 (205.3)	98.6–731 (365.4)	2500	-
TDS (mg/L)	3379–5018 (4369)	91–286 (129.4)	63–468 (233.8)	-	1000
Salinity (‰)	2.9–4.3 (3.7)	0.0–0.1 (0.01)	0.0–0.3 (0.1)	-	-
TH (mg/L of CaCO3)	470.7–979.0 (709.5)	51.5–243.5 (97.2)	59.1–308.5 (143.4)	-	1.5
Cl− (mg/L)	1100.8–2160.1 (1773.3)	9.2–34.2 (14.1)	6.8–47.9 (26.8)	250	250
F− (mg/L)	ND	0.02–0.10 (0.04)	0.04–0.07 (0.02)	1.2	1.5
NO2− (mg/L)	ND	0.01–0.02 (0.01)	0.1–2.0 (0.7)	0.5	0.5
NO3− (mg/L)	ND	3.2–16.5 (6.4)	2.2–71.3 (32.1)	50	50
SO42− (mg/L)	19.7–25.8 (22.3)	15.8–85.9 (30.1)	14.8–150.1 (41.2)	250	250
HCO3− (mg/L)	2453.1–3297.2 (2892.2)	81.4–162.0 (108.6)	101.2–330.1 (178.4)	-	-
Na+ (mg/L)	1571.5–2207.1 (1926.7)	7.0–36.2 (12.8)	7.4–37.3 (21.3)	200	200
K+ (mg/L)	60.1–180.9 (119.1)	0.3–6.6 (4.6)	0.7–41.7 (14.5)	-	-
NH4+ (mg/L)	ND	ND	0.1–0.7 (0.3)	0.5	-
Mg2+ (mg/L)	61.8–100.6 (76.7)	3.0–19.6 (7.8)	4.9–32.0 (10.7)	-	50
Ca2+ (mg/L)	46.4–265.1 (144.9)	15.7–73.0 (26.0)	14.7–95.2 (39.9)	-	75
Fe (mg/L)	1.1–1.4 (1.2)	0.07–0.14 (0.09)	0.05–0.68 (0.11)	0.2	2
Cu (mg/L)	ND	ND–1.3 (0.2)	ND	0.1	2
Zn(µg/L)	2.2–28.4 (13.8)	17.4–304.1 (63.1)	6.9–1661.1 (13.4)	5000	3000
Mn (µg/L)	ND	ND	ND	50	400
Ni (µg/L)	3.1–18.2 (11.7)	5.6–17.4 (11.7)	5.0–19.6 (14.2)	20	70
Cr (µg/L)	ND	ND	ND	50	50
Pb (µg/L)	ND	ND–3.5 (0.2)	4.1–23.1 (13.9)	10	10
Cd (µg/L)	ND	ND–0.8 (0.3)	0.9–3.8 (2.1)	5	3
222Rn (Bq/L)	9.6–24.8 (16.6)	no data	5.3–18.8 (11.1)	100 (5)	100 (3)/11.1 (4)
226Ra (Bq/L)	0.08–0.2 (0.18)	no data	0.07–0.25 (0.14)		0.1 (3)/0.185 (4)

⁽¹⁾ Maximum permissible limit for drinking water [50]; ⁽²⁾ threshold level for groundwater bodies used as drinking water from alluvial cone Rodnei Mountains (ROSO15) [51]; ⁽³⁾ WHO standard [53,59]; ⁽⁴⁾ EPA standard [60]; ⁽⁵⁾ Law 301/2015 [61].

Table 1. Summary of the analyzed parameters and the permissible limits for drinking water as specified by Romanian regulation and WHO guidelines (the bold values represent the permissible limits exceeding).

Parameter	Mineral Springs	Local Network	Private Wells	Romanian Standard (1,2)	WHO Standard (3)
pH	6.5–7.1 (6.8)	6.8–7.5 (7.1)	6.5–7.6 (7.2)	6.5–9.5	6.5–8.5
Eh (mV)	−24.9–11.8 (−6.5)	−47.7–7.9 (−24.3)	−54.3–7.5 (−29.9)	-	-
EC (µS/cm)	5280–7720 (6773)	141.8–447.1 (205.3)	98.6–731 (365.4)	2500	-
TDS (mg/L)	3379–5018 (4369)	91–286 (129.4)	63–468 (233.8)	-	1000
Salinity (‰)	2.9–4.3 (3.7)	0.0–0.1 (0.01)	0.0–0.3 (0.1)	-	-
TH (mg/L of CaCO3)	470.7–979.0 (709.5)	51.5–243.5 (97.2)	59.1–308.5 (143.4)	-	1.5
Cl− (mg/L)	1100.8–2160.1 (1773.3)	9.2–34.2 (14.1)	6.8–47.9 (26.8)	250	250
F− (mg/L)	ND	0.02–0.10 (0.04)	0.04–0.07 (0.02)	1.2	1.5
NO2− (mg/L)	ND	0.01–0.02 (0.01)	0.1–2.0 (0.7)	0.5	0.5
NO3− (mg/L)	ND	3.2–16.5 (6.4)	2.2–71.3 (32.1)	50	50
SO42− (mg/L)	19.7–25.8 (22.3)	15.8–85.9 (30.1)	14.8–150.1 (41.2)	250	250
HCO3− (mg/L)	2453.1–3297.2 (2892.2)	81.4–162.0 (108.6)	101.2–330.1 (178.4)	-	-
Na+ (mg/L)	1571.5–2207.1 (1926.7)	7.0–36.2 (12.8)	7.4–37.3 (21.3)	200	200
K+ (mg/L)	60.1–180.9 (119.1)	0.3–6.6 (4.6)	0.7–41.7 (14.5)	-	-
NH4+ (mg/L)	ND	ND	0.1–0.7 (0.3)	0.5	-
Mg2+ (mg/L)	61.8–100.6 (76.7)	3.0–19.6 (7.8)	4.9–32.0 (10.7)	-	50
Ca2+ (mg/L)	46.4–265.1 (144.9)	15.7–73.0 (26.0)	14.7–95.2 (39.9)	-	75
Fe (mg/L)	1.1–1.4 (1.2)	0.07–0.14 (0.09)	0.05–0.68 (0.11)	0.2	2
Cu (mg/L)	ND	ND–1.3 (0.2)	ND	0.1	2
Zn(µg/L)	2.2–28.4 (13.8)	17.4–304.1 (63.1)	6.9–1661.1 (13.4)	5000	3000
Mn (µg/L)	ND	ND	ND	50	400
Ni (µg/L)	3.1–18.2 (11.7)	5.6–17.4 (11.7)	5.0–19.6 (14.2)	20	70
Cr (µg/L)	ND	ND	ND	50	50
Pb (µg/L)	ND	ND–3.5 (0.2)	4.1–23.1 (13.9)	10	10
Cd (µg/L)	ND	ND–0.8 (0.3)	0.9–3.8 (2.1)	5	3
222Rn (Bq/L)	9.6–24.8 (16.6)	no data	5.3–18.8 (11.1)	100 (5)	100 (3)/11.1 (4)
226Ra (Bq/L)	0.08–0.2 (0.18)	no data	0.07–0.25 (0.14)		0.1 (3)/0.185 (4)

⁽¹⁾ Maximum permissible limit for drinking water [50]; ⁽²⁾ threshold level for groundwater bodies used as drinking water from alluvial cone Rodnei Mountains (ROSO15) [51]; ⁽³⁾ WHO standard [53,59]; ⁽⁴⁾ EPA standard [60]; ⁽⁵⁾ Law 301/2015 [61].

Mineral springs exhibited significantly higher values of EC, TDS and salinity compared to water from the local distribution network and private wells (Table 1), reflecting a higher concentration of inorganic salts—primarily Ca²⁺, Mg²⁺, K⁺, Na⁺, HCO₃⁻, Cl⁻, and SO₄²⁻—along with minor amounts of organic matter. In contrast, EC and TDS levels in local network and private wells water were within recommended safety limits (Table 1). According to TDS classification, water from the local supply and private wells falls within the freshwater category (TDS < 1000 mg/L), whereas the mineral spring water is classified as saline (3000 < TDS < 10,000 mg/L) [49]. The higher electrical conductivity (EC), total dissolved solids (TDS), and salinity in mineral spring waters compared to private wells and supply networks reflect intense water–rock interaction and longer residence times, a common feature of mineralized waters in Carpathian and Central European contexts [62]. Classification of mineral springs as saline (TDS > 3000 mg/L) aligns with European mineral-water surveys [62], which frequently categorize commercialized springs in this range [63], while private wells and network waters fit the “freshwater” class (TDS < 1000 mg/L).

Total hardness (TH) was calculated based on the concentration of calcium and magnesium. The mineral springs were classified as very hard waters, with TH values exceeding 180 mg CaCO₃/L [54,55,64]. In contrast, most samples from the local distribution network were moderately hard (60–120 mg CaCO₃/L), while water from private wells was generally hard (120–180 mg CaCO₃/L). Total hardness (TH) patterns also correspond to published values: Carpathian mineral springs are often “very hard” (>180 mg CaCO₃/L) owing to carbonate lithologies, whereas community supplies and wells in rural areas typically fall into “moderately hard to hard” categories, depending on aquifer depth and limestone/dolomite contributions [56,57]. Our results therefore mirror the broader regional hydrogeochemical trends and confirm the strong lithological control on hardness in the Carpathians.

The physico-chemical parameters remained relatively stable over time (Figure 2). The EC, TDS and salinity showed no significant seasonal variation. However, pH and TH were slightly lower during the spring sampling campaign (May 2018). The lack of strong seasonal variation in EC and TDS is also in agreement with hydrogeochemical monitoring in aquifers of the Carpathians, where buffering by carbonate reservoirs stabilizes ionic composition across seasons, with only minor springtime dilution effects observed in pH and hardness [56].

3.2. Major Ions Content

In groundwater from private wells and the local distribution system, the dominant cations and anions follow the order Ca²⁺ > Na⁺ > K⁺, Mg²⁺ and HCO₃⁻ > SO₄²⁻ > NO₃⁻, Cl⁻ > NO₂⁻, F⁻. In contrast, the mineral springs exhibit a different ionic composition, characterized by Na⁺ > Ca²⁺ > K⁺ > Mg²⁺ and HCO₃⁻ > Cl⁻ > SO₄²⁻ (Table 1). The concentration of major ions in all samples from the local supply network were within the permissible limits established by national drinking water standards.

However, 7%, 20% and 27% of private wells exceeded national limits for NH₄⁺, NO₂⁻ and NO₃⁻. The occurrence of nitrogenous compounds (NO₃⁻, NO₂⁻, NH₄⁺) in groundwater may be attributed to both natural processes—such as those governed by the nitrogen cycle—and anthropogenic sources, including leachate from septic systems, livestock waste, and agricultural runoff. Among these, diffuse agricultural pollution and the erosion of nitrogen-rich natural deposits are considered the primary contributors to nitrate contamination of groundwater [65,66]. Our findings that 7–27% of private wells exceeded national limits for NH₄⁺, NO₂⁻, and NO₃⁻ are consistent with European-scale evidence that agricultural diffuse pollution and inadequate sanitation are leading sources of nitrogenous compounds in groundwater. The European Environment Agency [67] reports that roughly 14% of monitoring stations across the EU exceed the 50 mg/L nitrate threshold, with rural wells in Eastern and Central Europe disproportionately affected.

In one of the wells, the calcium concentration exceeded the maximum recommended value set by the World Health Organization [53]. Elevated calcium levels in drinking water may lead to gastrointestinal discomfort and are generally undesirable for domestic use due to their potential to cause encrustation and scaling in household appliances [68]. Calcium concentrations exceeding WHO guidance in one well highlight localized geogenic influences. Elevated Ca²⁺ has also been documented in Apuseni karst aquifers [56] and in bottled European mineral waters [62], indicating that such anomalies are not uncommon in carbonate-dominated settings.

According to national standards for the exploitation and marketing of natural mineral waters [52], all investigated springs in the study area are classified as chlorinated waters (Cl⁻ > 200 mg/L), hydrogen carbonate waters (HCO₃⁻ > 600 mg/L), sodic waters (Na⁺ > 200 mg/L), and magnesium-rich waters (Mg²⁺ > 50 mg/L). Four springs also meet the criteria for calcium-rich waters (Ca²⁺ > 150 mg/L). These mineral springs hold therapeutic potential for internal use (drinking, aerosols, inhalations), parenteral administration (injections), and external treatments (bathing), but only under the strict supervision of qualified medical personnel. The results are relatively similar with other studies focused on hydrochemistry of mineral springs in EU [62]. The study performed on a total of 692 mineral waters from 13 countries showed that in terms of the ionic content, the dominant water type was bicarbonate, followed by fluoride, magnesium and calcium, and then sulphate and acidic had a lower prevalence [62].

Saline springs in the area are traditionally prescribed for digestive disorders (e.g., chronic gastritis), chronic bronchitis, chronic rhinitis, and for external therapies targeting musculoskeletal conditions, including inflammatory and rheumatic diseases [69,70,71]. Hydrogen carbonate-rich springs in the Sângeorz-Băi region may also be exploited economically through bottling and commercial distribution or used therapeutically in internal treatments for digestive and hepato-biliary disorders, as well as in external therapies such as inhalation and pulverization for respiratory conditions [69,70,71].

To further illustrate the hydrochemical type of the analyzed waters, a Piper diagram was constructed based on the major ions’ concentrations (meq/L) (Figure 3).

The investigated mineral springs are predominantly of the Na–HCO₃ and Na–HCO₃–Cl type, whereas most water samples from the local supply network and private wells correspond to the Ca–Na–HCO₃ type. This classification suggests that some private wells share a similar hydrochemical composition with the local supply network, potentially indicating a common aquifer or aquifers with comparable hydrogeochemical characteristics. The major ion composition of our local supply and private wells (Ca–Na–HCO₃ type) reflects typical shallow aquifers in the Carpathians, where carbonate dissolution governs the dominance of Ca²⁺ and HCO₃⁻, with secondary inputs from Na⁺ and SO₄²⁻ [56]. In contrast, the Na–HCO₃ and Na–HCO₃–Cl facies observed in our mineral springs correspond to hydrochemical signatures reported in highly mineralized or saline Carpathian springs, particularly in Transylvania and northern Romania, where evaporitic or deep-seated sources contribute to enrichment in Na⁺ and Cl⁻ [62].

Gibbs diagrams are commonly employed to evaluate the relationship between water chemistry and the lithological features of aquifers [72]. These diagrams help infer the dominant mechanisms influencing groundwater chemistry: rock-water interaction (rock dominance), evaporation, and precipitation [45,72]. In this study, Gibbs diagrams were constructed using two ratios: TDS versus (Na + K)/(Na + K + Ca), and TDS versus Cl/(Cl + HCO₃), where TDS is expressed in mg/L and ion concentrations in meq/L (Figure 4). The plotted diagrams (Figure 4), indicate that the hydrochemical evolution of groundwater from the local supply network and private wells is primarily controlled by rock weathering and water-rock interactions. In contrast, the chemical composition of the mineral springs appears to be influenced predominantly by evaporation processes. Notably, in the TDS versus (Na + K)/(Na + K + Ca) diagram, several mineral spring samples fall outside the defined fields, suggesting that anthropogenic activities may be affecting the concentrations of these ions.

3.3. Total Content of Metals

Water pollution by heavy metals is an increasingly significant global concern [73]. These elements are widely distributed in the environment, affecting water, air and soil, primarily due to anthropogenic activities such as industrial processes, agriculture, mining, and vehicular traffic. However, it is also essential to consider natural sources, including magmatic, metamorphic, and sedimentary rocks, which can contribute to background levels of these metals [74].

The concentrations of metals in the local water supply network were generally within permissible limits, except for Cu in a single sample (Table 1). The presence of higher Cu levels in the same sample across both sampling campaigns suggests a localized point source of contamination, potentially due to aging copper piping.

In contrast, several private wells exhibited concentrations of Fe and Pb that exceeded regulatory thresholds. Lead was detected in four wells, with three surpassing the acceptable safety limits. Lead is classified by IARC as possibly carcinogenic to humans. Chronic ingestion of high amounts of lead can adversely affect the kidneys, liver, spleen, and lungs. These wells should be subject to continuous monitoring to determine whether an accidental pollution source is present. In the absence of corrective measures, consumption of water from these sources should be either discontinued or significantly restricted to protect public health. The exceedance of Pb and NO₂⁻ limits in several wells has significant implications for public health and groundwater management. According to national legislation, the authorities must ensure access to water sources of adequate quality, which does not pose a risk to consumers health, to constantly monitor these water sources, and to provide free access to data related to monitors quality parameters. If locals want to use private wells as water sources, other than those monitored by the local authorities, they must be aware that they are assuming high risks. In this situation, the authorities have a major role, namely, to disseminate information on the water quality from the local distribution network and the negative impact on human health associated with the consumption of water of inadequate quality [75,76,77,78,79]. Academic community should also address this issue, by organizing different citizen science actions, together with local authorities. These actions could be focused on evaluating the water quality from private wells by performing specific analyses, disseminating the results, and raising awareness among locals related to the importance of water quality monitoring. Authorities can provide guidance related to possible solutions to improve water quality for private wells. Some of these solutions may require targeted interventions, such as point-of-use treatment (e.g., activated carbon filters for Pb, ion exchange or reverse osmosis for nitrate/nitrite) or may include stricter control of potential contamination sources (e.g., agricultural fertilizer usage).

The concentration of Cu, Pb, Cd, Cr, Ni and Mn in the analyzed mineral springs were all within the maximum limits established by national legislation for the exploitation and commercialization of natural mineral waters (1000 µg/L for Cu, 10 µg/L for Pb, 3 µg/L for Cd, 50 µg/L for Ni, 20 µg/L and 500 µg/L for Mn) [52].

The results indicate that the waters comply with safety standards for bottling as mineral water and for use in therapeutic treatment regimens. Iron concentrations were consistently below 10 mg/L, which does not satisfy the threshold for classification as ferruginous water, according to criteria established in previous studies [69,70,71]. No significant seasonal variations were observed in the concentrations of the analyzed metals. Slightly higher levels of Cu, Ni, Cd, and Fe were recorded during winter, whereas Zn concentrations showed a modest increase in spring.

To emphasize the trends and the relationships between the general physico-chemical parameters and the specific parameters (dissolved ions, heavy metals) and to identify the directions (principal components) along which the data variation is maximal, principal component analysis (PCA) was used (soft Past14.5) (Figure 5), which explained 68.3% of total variance by the first two principal components (PCs): PC1 represents 59.4% of the total variance in the water quality datasets and the PC2 represents 8.9%. The three clusters separated by the PCA consist in: (1) I1–I8; (2) F1, F2, F4, F5, F8–F11; (3) F3, F6, F7, F12–F15, R1–R7. Based on their distribution on PCA, the hydrochemical characteristics of cluster 1 are quite different from those of the other two clusters. The principal components did not indicate significant loadings between the analyzed parameters, the loading coefficients being lower than 0.6. In the present study, the higher loadings for PC2 had positive values for Cd (0.58), NO₂⁻ (0.37), NO₃⁻ (0.34), SO₄²⁻ (0.33), Ni (0.3) and negative for F⁻ (−0.33). For PC1 the higher loadings were positive in the case of CE, TDS, salinity, alkalinity, hardness, K⁺, Mg²⁺, HCO₃⁻, Fe (0.26), Ca²⁺ (0.24), ORP (0.23) while a negative loading was observed for pH (−0.23). As it is shown in Figure 5, these variables are very closed to each other’s, reflecting a strong correlation among them and a greater contribution to PC1, comparing to other variables. In the case of PC2, the parameters had a higher dispersion, which represents a weaker correlation among them. The PCA indicated that dissolved ions had a higher contribution to the hydrochemical characteristics of the analyzed water sources comparing to heavy metals (with the exception of Cd).

3.4. Radon and Radium Activity

Radon activity concentrations in mineral springs ranged from 9.6 Bq/L to 24.8 Bq/L, with an arithmetic mean of 16.6 Bq/L. In private wells, concentrations varied between 5.3 Bq/L and 18.8 Bq/L, with an average value of 11.1 Bq/L. The overall mean radon concentration across all samples was 13.07 Bq/L, which is slightly higher than the national average of 12.3 Bq/L reported in over 2000 samples collected across Romania [31,80]. These values are, however, consistent with those reported in previous studies, which indicate typical radon concentrations in groundwater ranging from 10 Bq/L to 50 Bq/L [81,82]. Earlier research also supports the observation of higher radioactivity levels in these waters compared to other Romanian water sources [83]. The safe level recommended by [60] for radon in drinking water is 11.1 Bq/L, while WHO recommends a maximum permitted limit of 100 Bq/L [53,59], which aligns with the current Romanian national legislation [61].

Radium activity was also found to be slightly higher in mineral springs, with values ranging from 0.08 Bq/L to 0.28 Bq/L and an average of 0.18 Bq/L, compared to 0.07 Bq/L to 0.25 Bq/L (mean 0.148 Bq/L) in private wells. In 29% of the analyzed samples, radium activity exceeded the EPA’s recommended limit of 0.185 Bq/L [60]. When compared to the more stringent WHO guideline of 0.1 Bq/L [59] 83% of the samples surpassed this threshold, indicating a widespread exceedance of international safety standards for radium content in drinking water.

Considering that the activity concentrations of the investigated radioisotopes fall within the limits established by the national regulations and guidelines for radon [59], as well as the standards for radium [60], their presence in the analyzed water sources is not expected to pose a significant risk to human health or to the environment.

3.5. Water Suitability for Drinking Usage

The analysis showed that 53% of private well water samples exceeded permissible limits for several chemical parameters, including NO₂⁻, NO₃⁻, NH₄⁺, Ca²⁺, Pb, and Fe. By contrast, only one sample from the municipal distribution system exhibited an elevated Cu concentration, exceeding the recommended threshold. To evaluate the potential health risks associated with ingestion of these constituents through drinking water, estimated daily intakes were calculated and compared with guideline values established by relevant health authorities (Table 2).

As expected, the intake of mineral nutrients through water ingestion was substantially higher for mineral spring waters. The estimated daily intake of Na⁺ and Cl⁻ exceeded the adequate intake levels recommended for human consumption (Table 2). Consequently, such waters are unsuitable for routine drinking. Instead, they are more appropriate for therapeutic applications -such as the treatment of digestive disorders, chronic bronchitis, and chronic rhinitis -administered in specific doses over short periods (typically 7–10 days) under the supervision of qualified medical personnel. Mineral waters with elevated salinity are also commonly used in external therapies, particularly for musculoskeletal disorders. However, prolonged and continuous consumption of drinking water with high Na⁺ and Cl⁻ concentrations may pose health risks, notably by contributing to the onset or progression of cardiovascular conditions.

In one of the analyzed private wells, the EDI of NO₂⁻ exceeded the acceptable daily intake (ADI) established by the European Commission’s Scientific Committee on Food (SCF) [84,85] (Table 2). This finding indicates that continuous consumption of water from this source poses a significant health risk. Nitrites are classified by the International Agency for Research on Cancer (IARC) as Group 2A agents, meaning they are probably carcinogenic to humans. Furthermore, epidemiological studies have linked nitrite exposure to adverse health outcomes such as methemoglobinemia (commonly known as “blue baby syndrome”), gastric cancer, thyroid disfunction, and diabetes [68]. Consequently, the use of water from this well for drinking purposes should be discontinued. In the remaining private wells where the concentrations of NO₃⁻, NH₄⁺, Ca²⁺, Pb and Fe exceeded the maximum allowable limits, the corresponding EDIs remained below health-based guideline values. Nonetheless, it is recommended that these sources be used with caution and that their use for drinking purposes be reduced, particularly for vulnerable populations such as infants and individuals with pre-existing health conditions.

Table 2. Groundwater suitability for drinking based on the concentrations of major ions and trace metals (the bold values represent the exceeding of the recommended values).

Parameter	EDI (µg/kg bw/day)			Recommendation (µg/kg bw/day)
	Mineral Springs	Local Supply System	Private Wells
F−	ND	0.67–3.33 (1.38)	1.5–2.33 (2.1)	56.66 (1)
NO2−	ND	0.3–0.5 (0.3)	4.0–68.1 (23.8)	60 (3)/70 (4)
Fe	37.9–42.8 (40.85)	2.56–4.13 (3.02)	2.18–12.9 (3.63)	800 (9)
Zn	0.26–0.79 (0.46)	0.50–9.06 (2.10)	0.26–50.98 (4.46)	300–1000 (9)
Ni	0.18–0.60 (0.39)	0.21–0.52 (0.39)	0.22–0.63 (0.48)	11(10)/2.8 (11)
Pb	ND	0.01–0.12 (0.02)	0.24–0.71 (0.47)	3.57 (12)
Cd	ND	0.01–0.03 (0.01)	0.02–0.12 (0.06)	0.83 (13)
	EDI (mg/kg bw/day)			Recommendation (mg/kg bw/day)
Cl−	46.36–67.84 (59.11)	0.34–0.79 (0.47)	0.23–1.48 (0.89)	38.3–41.7 (2)
NO3−	ND	0.13–0.46 (0.21)	0.07–2.33 (1.07)	3.7 (4)
Na+	52.76–71.74 (64.22)	0.29–0.81 (0.43)	0.28–1.09 (0.71)	25 (5)
K+	2.59–5.29 (3.97)	0.08–0.19 (0.11)	0.09–1.22 (0.45)	58.3 (6)
Mg2+	2.16–3.19 (2.56)	0.17–0.46 (0.26)	0.18–0.88 (0.36)	5.8 (7)
Ca2+	2.67–5.82 (5.25)	0.54–1.51 (0.87)	0.50–2.48 (1.33)	15.83 (8)
Cu	ND	0.00007–0.04 (0.006)	ND	0.5 (9)

⁽¹⁾ Based on the Adequate Intake (AI) of 3.4 mg/day for an adult male [86]; ⁽²⁾ based on the adequate intake of 2300–2500 mg/day for all adults [87]; ⁽³⁾ acceptable daily intake (ADI) recommended by the European Commission’s Scientific Committee on Food (SCF) [84,85]; ⁽⁴⁾ acceptable daily intake (ADI) recommended by the Joint Expert Committee of the Food and Agriculture (JEFCA) of the United Nations/World Health Organization (WHO) [88,89]; ⁽⁵⁾ based on the adequate intake of 1500 mg/day was set for all adults [86]; ⁽⁶⁾ based on the Adequate Intake (AI) of 3500 mg/day for an adult male [90]; ⁽⁷⁾ based on the Adequate Intake (AI) of 350 mg/day for adult male [90]; ⁽⁸⁾ based on the Population Reference Intake (PRI) of 950 mg/day for an adult male [90]; ⁽⁹⁾ PMTDI (Provisional Maximum Tolerable Daily Intake) [91]; ⁽¹⁰⁾ TDI (Tolerable Daily Intake) [92]; ⁽¹¹⁾ TDI [93]; ⁽¹²⁾ TDI [94]; ⁽¹³⁾ provisional tolerable daily intake based on the provisional tolerable monthly intake of 25 µg/kg by [91].

Table 2. Groundwater suitability for drinking based on the concentrations of major ions and trace metals (the bold values represent the exceeding of the recommended values).

Parameter	EDI (µg/kg bw/day)			Recommendation (µg/kg bw/day)
	Mineral Springs	Local Supply System	Private Wells
F−	ND	0.67–3.33 (1.38)	1.5–2.33 (2.1)	56.66 (1)
NO2−	ND	0.3–0.5 (0.3)	4.0–68.1 (23.8)	60 (3)/70 (4)
Fe	37.9–42.8 (40.85)	2.56–4.13 (3.02)	2.18–12.9 (3.63)	800 (9)
Zn	0.26–0.79 (0.46)	0.50–9.06 (2.10)	0.26–50.98 (4.46)	300–1000 (9)
Ni	0.18–0.60 (0.39)	0.21–0.52 (0.39)	0.22–0.63 (0.48)	11(10)/2.8 (11)
Pb	ND	0.01–0.12 (0.02)	0.24–0.71 (0.47)	3.57 (12)
Cd	ND	0.01–0.03 (0.01)	0.02–0.12 (0.06)	0.83 (13)
	EDI (mg/kg bw/day)			Recommendation (mg/kg bw/day)
Cl−	46.36–67.84 (59.11)	0.34–0.79 (0.47)	0.23–1.48 (0.89)	38.3–41.7 (2)
NO3−	ND	0.13–0.46 (0.21)	0.07–2.33 (1.07)	3.7 (4)
Na+	52.76–71.74 (64.22)	0.29–0.81 (0.43)	0.28–1.09 (0.71)	25 (5)
K+	2.59–5.29 (3.97)	0.08–0.19 (0.11)	0.09–1.22 (0.45)	58.3 (6)
Mg2+	2.16–3.19 (2.56)	0.17–0.46 (0.26)	0.18–0.88 (0.36)	5.8 (7)
Ca2+	2.67–5.82 (5.25)	0.54–1.51 (0.87)	0.50–2.48 (1.33)	15.83 (8)
Cu	ND	0.00007–0.04 (0.006)	ND	0.5 (9)

⁽¹⁾ Based on the Adequate Intake (AI) of 3.4 mg/day for an adult male [86]; ⁽²⁾ based on the adequate intake of 2300–2500 mg/day for all adults [87]; ⁽³⁾ acceptable daily intake (ADI) recommended by the European Commission’s Scientific Committee on Food (SCF) [84,85]; ⁽⁴⁾ acceptable daily intake (ADI) recommended by the Joint Expert Committee of the Food and Agriculture (JEFCA) of the United Nations/World Health Organization (WHO) [88,89]; ⁽⁵⁾ based on the adequate intake of 1500 mg/day was set for all adults [86]; ⁽⁶⁾ based on the Adequate Intake (AI) of 3500 mg/day for an adult male [90]; ⁽⁷⁾ based on the Adequate Intake (AI) of 350 mg/day for adult male [90]; ⁽⁸⁾ based on the Population Reference Intake (PRI) of 950 mg/day for an adult male [90]; ⁽⁹⁾ PMTDI (Provisional Maximum Tolerable Daily Intake) [91]; ⁽¹⁰⁾ TDI (Tolerable Daily Intake) [92]; ⁽¹¹⁾ TDI [93]; ⁽¹²⁾ TDI [94]; ⁽¹³⁾ provisional tolerable daily intake based on the provisional tolerable monthly intake of 25 µg/kg by [91].

Water quality parameters from the local distribution network, as well as from 47% of the sampled private wells, were within the regulatory limits. The EDIs for all analyzed substances in these sources were also below recommended thresholds, indicating that these water sources are safely for human consumption. Ensuring access to high-quality drinking water is particularly important in regions such Sângeorz-Băi, where tourism constitutes a primary economic activity. The availability of safe and reliable drinking water is essential for both public health and sustainable development of the local tourism industry.

For all analyzed water samples, the committed effective dose resulting from the ingestion of ²²²Rn (

Table 3. Estimated committed effective dose (CED) for adults resulting from the ingestion of drinking water containing radon (²²²Rn) and radium (²²⁶Ra).

Source	Average Value of Estimated Committed Effective Dose (mSv/year)
	222Rn	226Ra
Mineral springs	0.035–0.089 (0.060) (1) 0.012–0.031 (0.021) (2)	0.009–0.022 (0.020) (3) 0.007–0.017 (0.015) (4)
Private wells	0.021–0.073 (0.043) (1) 0.007–0.025 (0.015) (2)	0.007–0.025 (0.014) (3) 0.006–0.019 (0.011) (4)
Recommendations (5)	1	0.1

⁽¹⁾ Based on conversion factor recommended by UNSCEAR [35]; ⁽²⁾ based on conversion factor recommended by IAEA [36]; ⁽³⁾ based on conversion factor recommended by IAEA [36]; ⁽⁴⁾ based on conversion factor recommended by WHO [38]. ⁽⁵⁾ based on WHO recommendation [59].

), remained below the recommended annual limit of 1 mSv/year [59]. This value represents less than half of the average global exposure to natural background radiation, which is approximately 2.4 mSv/year. Regarding ²²⁶Ra, the results indicate that the daily ingestion 1 L of water from the studied sources does not pose a radiological health risk to consumers. The mean committed effective dose from ²²⁶Ra ingestion (Table 3) was significantly lower than the WHO recommended annual internal dose limit of 0.1 mSv/year [59]. Overall, the ingestion-related doses from both radionuclides were negligible when compared to other natural sources of radiation exposure, such as indoor radon inhalation or the ingestion of naturally occurring radionuclides like ⁴⁰K.

3.6. Water Suitability for Agriculture Usage

In this study, the suitability of water from private wells and the local supply system for irrigation was evaluated, while mineral springs were excluded due to their high concentrations of dissolved ions. A summary of the results is presented in

Table 4. Groundwater suitability for irrigation (the suitability class is marked in bold, according to the values obtained for each quality parameter).

Parameter	Local Supply System	Private Wells	Suitability
EC (µS/cm)	141.8–447.1 (205.3)	98.6–731.0 (365.4)	excellent (<250), good (250–750), permissible (750–2000), doubtful (2000–3000), not suitable (>3000) [95,96]
TDS (mg/L)	91–286 (129.4)	63–468 (233.8)	desirable (<500), permissible (50–1000), useful for irrigation (1000–3000), unfit for irrigation (>3000) [95,96]
TH (mg/L of CaCO3)	51.5–243.5 (97.2)	59.1–308.5 (143.4)	soft (<75), moderately hard (75–150), hard (150–300), very hard (>300); or: soft (<60), moderately hard (60–120), hard (121–180), very hard (>180) [95,96]
SAR	0.4–0.8 (0.5)	0.5–1.1 (0.8)	excellent (<10), good (10–18), doubtful (18–26), not safe (>26) [39,45,96]
%Na	22–27 (24)	22–49 (31)	excellent (<20), good (20–40), permissible (40–60), doubtful (60–80), not safe (>80) [40,96]
KR	0.23–0.33 (0.27)	0.18–0.65 (0.35)	suitable (<1), unsuitable (>1) [41,95,96]
RSC	−1.07–0.45 (−0.17)	−1.49–1.26 (0.05)	suitable (<1.25), marginally suitable (1.25–2.5), not suitable (>2.5) [96,97]
MAR	29–39 (33)	22–45 (32)	suitable (<50), not suitable (>50) [43,96]
PI	59–104 (81)	46–107 (75)	good (<80), moderate (80–100), poor (10–20) [95,96]

. Although most samples were classified as moderately hard or hard waters, the concentrations of Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl⁻, and HCO₃⁻ did not present significant risks to crops. Based on the calculated indices, the majority of sources were classified as having excellent, good, or acceptable quality for irrigation (Table 4).

4. Conclusions

This study provides a comprehensive, multidisciplinary assessment of groundwater quality in the Sângeorz-Băi area, a former emblematic spa region of Romania. Private wells, the municipal supply, and mineral springs remain central to drinking water provision, therapeutic practices, and socio-economic development. By integrating hydrochemical, radiological, toxicological, and irrigation suitability analyses, the study yields conclusions of direct relevance to public health, water management, and sustainable regional development.

Groundwater from the municipal network generally complies with regulatory standards. In contrast, more than half of the private wells exceeded permissible limits for NO₃⁻, NO₂⁻, NH₄⁺, Pb, and Fe. One well showed acute nitrite contamination, representing an immediate health risk that requires discontinuation of use. Elevated Pb and Fe levels highlight the vulnerability of aquifers to diffuse agricultural inputs and infrastructure deficiencies. Mineral springs complied with regulatory limits for trace metals and radionuclides, but their high Na⁺ and Cl⁻ concentrations make them unsuitable for continuous consumption. They remain valuable for short-term therapeutic use under medical supervision and retain potential for economic exploitation through bottling. Radiological analyses indicated radon activities below international safety thresholds. Radium occasionally exceeded the stricter WHO guideline, requiring continued monitoring but not indicating immediate health risks.

The findings underscore the dual role of groundwater in the region: a critical source of safe drinking water under regulated conditions, but also a vector of contamination where private wells remain unmonitored. Effective protection requires systematic water quality monitoring, stricter regulation of agricultural practices, infrastructure improvements, and increased community-level risk awareness.

A key limitation of this study lies in the restricted temporal coverage of sampling, which was conducted only twice (autumn 2017 and spring 2018). Although these campaigns provide valuable insights under contrasting seasonal conditions, they do not capture the full extent of seasonal or inter-annual variability in groundwater quality. Long-term monitoring is therefore required to achieve a more comprehensive characterization of temporal dynamics.

In conclusion, this study advances the understanding of groundwater quality in a complex hydrogeological and socio-economic setting. It also provides a replicable framework for groundwater management in spa and rural regions facing similar challenges at the intersection of environment, public health, and sustainable development.